Empty @viewport should not override legacy viewport.

Source/core/css/resolver/ScopedStyleResolver.cpp

Index: Source/core/css/resolver/ScopedStyleResolver.cpp
diff --git a/Source/core/css/resolver/ScopedStyleResolver.cpp b/Source/core/css/resolver/ScopedStyleResolver.cpp
index cb60fdc2797d8951a99328e1a12bb8ff11abd8cb..ab6755e20fdc8f70d1457d3b185aeba0c8101e63 100644
--- a/Source/core/css/resolver/ScopedStyleResolver.cpp
+++ b/Source/core/css/resolver/ScopedStyleResolver.cpp
@@ -34,6 +34,7 @@
 #include "core/css/RuleSet.h"
 #include "core/css/StyleRule.h"
 #include "core/css/resolver/StyleResolver.h" // For MatchRequest.
+#include "core/css/resolver/ViewportStyleResolver.h"
 #include "core/dom/Document.h"
 #include "core/dom/shadow/ElementShadow.h"
 #include "core/dom/shadow/ShadowRoot.h"
@@ -427,8 +428,10 @@ void ScopedStyleResolver::matchPageRules(PageRuleCollector& collector)
 
 void ScopedStyleResolver::collectViewportRulesTo(StyleResolver* resolver) const
 {
+    // Only consider the global author RuleSet for @viewport rules.
+    ASSERT(m_scopingNode.isDocumentNode());
     if (m_authorStyle)
-        resolver->collectViewportRules(m_authorStyle.get(), StyleResolver::AuthorOrigin);
+        resolver->viewportStyleResolver()->collectViewportRules(m_authorStyle.get(), ViewportStyleResolver::AuthorOrigin);
 }
 
 } // namespace WebCore